This is a really nice and well made game, plus a really unique take on the jam's theme. You've got some really great pixelated graphics and UI (Though I think there were missing images in the tutorial), they were charming and pleasing to look at. The gameplay itself was also extremely fun, and I found it really satisfying to chain in multiple flies at once, that's some good game design. There was good use of sound effects and the controls felt good and easy to learn and understand.
One thing to note is that I can stand still and have multiple flies fly into me, though not efficient to eat flies I feel there should be more of an incentive to get the player to move around and use the web more; you could have a system that makes the flies avoid/fly away from the spider. The abdomen enlarging to indicate how much web you have left is also pretty good, however it still wasn't too clear how much web I have (I was able to spam click the space button and still reel in a ton of flies). You could probably maintain this scaling mechanic but make it a bit more clearer by having the abdomen as a separate object and then scaling it according to how much web you have left. There also seemed to be a bug when I ended a game, and I couldn't click any UI buttons.
This is a super cool submission that I had a ton of fun playing, and good luck on the rest of the jam!